This invention relates to a braking system particularly suited to construction machines and more particularly to a reliable braking system which prevents unintended braking or loss of braking capability upon malfunction or failure of certain functional components of the braking control system.
The need for a reliable service and parking brake system in large construction machines is increasingly important as these machines increase in size. It is also desirable that unintentional application of the service and parking brakes be avoided. Failure or malfunction of certain elements of service and/or parking brake control systems can result in unintentional braking. Unintentional braking is objectionable and some governmental jurisdictions prohibit operation of vehicles having barking systems that allow unintentional braking upon component malfunction or failure in the braking system. As the size of construction machines has increased, the noise to which the operator is subjected has also increased. Although insulation of the operator""s cab reduces the noise level, there is a significant amount of noise transmitted to the cab by mechanical and fluid control apparatus and through openings for mechanical controls and fluid hoses extending into the cab. The various mechanical linkages and controls mounted in or extending into the cab complicates installation of the cab during manufacture of the construction machine. There is also a need to provide remote control for construction machines, such as for those operating in a hazardous or unhealthy environment.
Electro-hydraulic valves are used in a service brake control system disclosed in U.S. Pat. No. Re; 36,152 reissued on Mar. 16, 1999 to J. Hosseini et al for a Method and Apparatus for Controlling Differentially Driven Wheel-Slip for an Articulated Machine. The service brakes of this system are described as being either fluid pressure applied and spring-biased in a disengaged position or spring-biased in the engaged position and maintained in the disengaged position by fluid pressure. Upon failure or malfunction of certain components of this system, the brakes may be applied without the intention of the operator.
U.S. Pat. No. 5,749,633 issued May 12, 1998 to E. Bumgartner for a Brake by Wire System discloses use of a pair of electro-hyraulic valves in a braking system having a conventional master cylinder and an ABS/TCS brake controller supplemented by a brake by wire controller. Automotive master cylinders are not suitable for use in large construction machines and malfunction or failure of certain elements of this automotive braking system could result in unintentional application of one or more of the service brakes.
The present invention is directed to overcoming one or more of the problems as set forth above.
Each wheel of an axle of a construction machine is provided with a pressure fluid applied and spring released service brake which is actuated by pressure fluid delivered through an electrically controlled service valve. Pressure fluid is delivered to the service valves for the service brakes of the two wheels on the axle through an electrically controlled safety valve connected in pressure fluid receiving relation to a source of pressure fluid. The two service valves and the safety valve are controlled by an electric control which includes signal lines extending to a manually operated signal generating control in the cab. The service valves and the safety valve must all be shifted from their normally closed positions to open positions in order to apply the service brakes. This valve arrangement avoids unintentional application of the service brakes upon certain malfunctions or failures of components of the braking system. This braking arrangement also permits safe braking even if the safety valve locks up in an open position. A spring applied and pressure released parking brake may be provided on a transmission output shaft, the parking brake being released by pressure fluid delivered through an electrically controlled parking valve which is in turn controlled by a parking brake switch in the operator""s cab.
The electric control for the braking system may include a primary electronic control module and, for safety purposes, a back-up electronic control module, both of which are preferably located on the machine outside the cab. Two sources of electric power and two sources of pressure fluid may be provided to ensure safe operation of the machine. The braking system of this invention is a brake by wire system with brake operating apparatus moved out of the cab and onto the chassis of the construction machine. This reduces the noise level in the cab and simplifies installation of the cab during manufacture of the machine.